Find two identical waveforms that sound different.That would be an instance of a difference you can hear, but you cannot measure. That would be the only thing that counts as such an instance.If the waveforms look different on a scope with the highest resolution possible by the current state of the art, then you *can* measure the differences. If they look idential, then you can't measure the differences. It's difficult for me to see how it is somehow 'Hard Line' to say that any audible difference can be measured in the complete, utter, and total absence of even one example of an audible difference between two signals that cannot be seen on a scope. It is true that, throughout history, scientists have made some arrogant claims about what they thought they knew. That does not prove that all knowledge is suspect. The basic principles of, say, Newtonian physics have been taken as known and given for centuries, and they still hold true today. There are some things that can be known and measured. If you ever get behind the wheel of a car, or ride in an airplane, you are trusting your life to the fact that Newtonian physics will continue to hold true. Most of us do so daily.It seems well and good to tag people who trust facts with a derogatory epithet like 'Hard Line', characterizing them as being fanatical religeous adherents to some philosophy. But, ironically, it seems much more 'Hard Line' to staunchly hold to a belief for which there is no supporting evidence whatsoever. There are a lot of enlightened papers about differences that can or cannot be heard, and people in the field argue about just how good Human hearing is at discerning such differences. I know of no respectible theorist in the science of auditory perception that thinks there can be audible differences between two signals that cannot be quantified, though.Certainly, not everything can be known. That doesn't make everybody who trusts what *is* known into a religeous fanatic.Regards, --Dan